In known injection devices, such as wind-up pens, based on torsion springs, the use of dial-down mechanisms rely on that the user of the injection device applies a force to a rotatable dose setting member of the injection device. The force must be applied in order to axially withdraw the dose setting member a certain distance to release the dose setting member from a toothing mechanism or ratchet positioned within the body of the injection device. By releasing the dose setting member from this toothing mechanism the dose setting member can be reversed by rotation and set at a new and lower dose.
An example of a known wind-up pen applying a torsion spring may for example be found in U.S. Pat. No. 5,104,380. However, the pen suggested in U.S. Pat. No. 5,104,380 does not offer a dial-down mechanism. A dial-down mechanism is provided in WO 02/053214. However, the proposed solution in WO 02/053214 involves a linear spring.
It is a disadvantage of known torsion spring-based dial-down systems that the user must apply a force to withdraw the dose setting member a certain axial distance and, at the same time, adjust the angular position of the dose setting member. Especially for persons having reduced motoric skills or reduced finger strength, such as children, elderly people or disabled people this is a rather complicated procedure.
US 2004/199117 discloses a medication delivery pen including an arrangement where incorrect dosage settings may be corrected by a user via a dial-back feature that enables the user to reset the dose amount without expelling medication and without having to dial a dose knob to an extended, reset position. The medication delivery pen of US 2004/199117 is a so-called manual pen where the injection of a medicament from the pen is driven by a force purely provided by the user of the pen. Thus, the injection of a medicament is not assisted by any resilient member, such as a spring, and the dial-down arrangement disclosed in US 2004/199117 is not arranged to maintain a resilient member in a given strained position.
It is an object of the present invention to provide a dial-down mechanism for automatic wind-up pens. Automatic wind-up pens are here to be understood as pens having a resilient member, such as a spring, to assist injecting a medicament from an injection device.